i dunno guys i got one and my strike rate went up %30 on clones. sure you can get away without it but don't let anyone tell you they're a waste of money. it's proven that seedilings and clones have specific temperatures they thrive at. the heating mat will allow you to dial in the temperature exactly.
best temps for clones 74f-79f
my temps w/mat= 77f <----------- %100 sucess
without mat= 69f <----------- %70 sucess